This invention relates to systems for planning and adjusting the mission profiles of aircraft and more particularly to systems and methods for planning the mission profiles of aircraft so that the controlled aircraft reaches a predetermined waypoint at a required time of arrival.
In today""s world, transportation by aircraft is extremely popular. This popularity has resulted in dramatic increases in air traffic and caused a variety of related difficulties including airborne traffic congestion and overburdening of aircraft ground support facilities. It is estimated that air traffic will continue to grow, causing the further exacerbation of these problems. To effectively manage aircraft traffic congestion, both in the air and on the ground, various authorities are exercising, or are seeking to exercise, increasing control over the operation of aircraft within their jurisdictions. This increasing level of control already extends to the assignment of aircraft flight paths and the imposition of specific time constraints upon aircraft operators.
Contemporaneously with the increase in flight volume, competition between commercial aircraft operators has also increased and is expected to increase further. This competition has created a situation where aircraft operators must exercise tight control over their operating expenses to remain profitable. Experience has shown that aircraft operating expenses are significantly impacted by consumption of fuel, as well as utilization of aircraft equipment, flight crew and other personnel. These, in turn, are significantly impacted by factors that combine to form the aircraft mission including the flight duration, flight speed, flight path, and takeoff and landing cycles. Thus, to effectively control operating costs, aircraft operators are demanding increased control over the planning and execution of their missions. It naturally follows then, that aircraft operators who enjoy greater autonomy and control over the planning and execution of their missions will be rewarded in the marketplace.
Typically, an aircraft operator""s use of an aircraft may be described in terms of the execution of a series of missions, each mission comprising one takeoff from an origination location, one landing at a destination location, and a period of airborne flight between the takeoff and the landing. The set of flight positions and flight velocities traversed by the aircraft in the performance of a particular mission may then be described as a mission profile. Typically, the position of an aircraft during flight may be described in terms of a three dimensional translation from some arbitrary reference point. Typically, the aircraft""s latitude, longitude and altitude are used. Further, the aircraft""s orientation may be described in terms of its angular rotation about three reference axis, for example, pitch, yaw, and roll. The aircraft""s velocity may be described as a vector having a direction or heading component and a magnitude or speed.
The portion of the mission between the takeoff and the landing may be further described in terms of a series of flight phases. The first of these phases is typically referred to as the climb phase. In climb, the vertical component of the aircraft""s position increases substantially as the aircraft ascends from the takeoff elevation to a cruise altitude. A second phase is frequently referred to as cruise. In the cruise phase, the vertical component of the aircraft""s position remains relatively constant at the cruise altitude. Cruise is typically the phase during which the aircraft occupies the majority of the duration of its missions. A third phase is commonly referred to as descent, wherein the vertical component of the aircraft""s position decreases substantially as the aircraft descends from the cruise altitude to an approach altitude. An approach phase typically follows descent and is followed by the landing phase. Typically, an aircraft in the approach phase follows a flight path that is substantially level or that is declining in altitude. The altitudes followed in approach are typically between 5000 and 10000 feet above sea level, often depending on the elevation of the destination airport.
In approach, aircraft has entered the near proximity of their destination airport. This proximate region is called the terminal area. The terminal area extends approximately 30 miles in radius from most major airports and is defined in large part by predetermined boundaries prescribed by the relevant authority, in some part by the range of the airport""s terminal approach radar. When an aircraft enters the terminal area, authority for its control transfers from an air traffic control center to the terminal area controller. The point at which control is transferred is called the transition point.
In addition to exhibiting the distinctive characteristics described above, each phase may also entail aircraft operational limitations that are inherent in the specific combination of the aircraft and its powerplant. These aircraft operational limitations may be influenced by a variety of factors including aircraft structural considerations such as wing loading and flutter; aircraft powerplant considerations such as thrust, fuel consumption, life, air-starting and/or bleed pressure; aircraft aerodynamic considerations such as lift, drag and stall; as well as system control and stability characteristics. These aircraft operational limitations have the capability to inhibit aircraft autonomy and affect aircraft controllability.
As briefly mentioned above, aircraft operators typically desire to retain or regain maximum autonomy with respect to the planning and execution of their missions. Aircraft operators who enjoy full aircraft autonomy are free to select and/or adjust the combination of flight positions and velocities that make up their mission profile to suit their individualized objectives. Those objectives may relate to considerations such as time, payload, position, and/or cost. Operators enjoying full autonomy will be more capable to continually improve their operating efficiencies as well as their payload capacity, range and/or profitability.
To improve safety and reduce congestion, however, it has become increasingly necessary to impose restrictions and constraints upon aircraft operators, tending to diminish the scope of their aircraft autonomy. Some limitations may have been operator-imposed, such as instrument-only flight restrictions, under which operators who are unable to operate safely and efficiently without the aid of instrumentation may voluntarily restrict their operations. Other limitations may have been legislated, for example, through the imposition of air traffic restrictions by designated authorities. Due to increased air traffic, the expansion of both the scope and duration of legislated restrictions is commonly viewed as the only currently viable means of reliably ensuring aircraft separation, preventing airport congestion, maintaining special-use airspace zones, and in general, ensuring flight safety. This solution, however, is inherently undesirable due to its infringement upon aircraft autonomy.
As a result, significant efforts have been directed toward the development of technology that would accommodate increased air traffic and ensure safety without unnecessarily imposing upon aircraft autonomy. One solution has been the development of control systems that enable operators to reliably reach a predetermined waypoint at, or close in time to, a negotiated, predetermined time of arrival. Admittedly, it is an intrusion upon the autonomy of the aircraft operators to be required to commit to reaching specific waypoints at predetermined times. Nevertheless, some concession of autonomy may be tolerated for the sake of maintaining safety. Required time of arrival control systems are able to satisfy the needs to reduce ground and air-based congestion while simultaneously providing aircraft operators with a relatively high degree of aircraft autonomy.
As air traffic increases, and as the desire for aircraft autonomy also increases, the need for such systems to be enhanced with additional time control authority also increases. It is widely accepted.that operators who reliably and accurately meet their time of arrival commitments will likely receive preferential routing treatment and, therefore, will be able to achieve lower operating costs. Such preferential treatment will also likely include more autonomy as well as the assignment of more direct routes or other preferential treatment such as assignment of trajectories, or missions, that benefit from tail winds.
Increasingly, the terminal area is becoming very tightly controlled. Thus the use of required time of arrival controls may not be useful within the terminal area within the near future. Nevertheless, required time of arrival controls may also be used to achieve scheduled border crossings, checkpoints, or to establish the initial spacing of aircraft entering the terminal area.
A variety of systems are currently available for enabling an aircraft to arrive at a predetermined waypoint substantially at a predetermined time, also known as a required time of arrival (RTA). Unfortunately, however, these prior art systems are deficient in many respects. For example, these current systems are limited in their ability to enable an aircraft to reliably reach the waypoint within a tolerable margin of the RTA, such as, for example within about 30 seconds. This 30 second accuracy, however, is too large for reliable use within the terminal area, which demands a tighter tolerance due to the increased traffic within the terminal area. Further, some current systems are limited in their ability to accommodate dynamic atmospheric effects such as wind, temperature, and/or pressure variations. Moreover, prior art systems are typically capable of automatically adjusting the aircraft""s speed only while the aircraft is flying the cruise phase of the mission. These limitations makes it difficult, if not impossible, for such prior art systems to enable an aircraft to reliably reach a predetermined waypoint in the terminal area, and often in the descent or approach phases, substantially at the RTA, e.g., preferably within 6 seconds. Also, prior art systems are typically limited to a specific chosen method of adjusting the speed profile, such as modifying the cost index, or such as adding a constant speed change along a trajectory.
For example, U.S. Pat. No. 5,408,413, which is hereby incorporated by reference for background purposes, discloses such a control system but is limited in its effectiveness due to the manner in which it accomplishes speed modulation. This system modulates speed in such a manner as to maintain a constant ground speed change across all of the flight segments. This system is moderately effective for the cruise segment where aircraft speed may be adjusted significantly without the imposition of an aircraft operational limitation. In the climb, descent, and approach phases, however, the ability of such control systems to modulate aircraft speed is much more likely to be inhibited by one or more aircraft operational limitations. Further, whenever a commanded speed modulation would cause an aircraft operational limitation to be exceeded, a non-linearity will result. In other words, the command will not be performed as expected. As a result, such control systems may be ineffective in modulating speed, may become unstable, and if implemented digitally, may fail to reach a converged solution that may be reliably expected to achieve its intended result within the requisite period of time. This system may also produce a speed profile that is not fuel optimal.
As a further example, U.S. Pat. No. 5,121,325, which is also hereby incorporated by reference for background purposes, relies upon an equivalent range approximation to estimate the effects of changing an independent parameter that is related to operating cost, and indirectly affects the speeds in a resulting mission profile and the anticipated time of arrival. Although this system is able to discover a solution quickly, it relies upon an approximated mission profile resulting in a significant compromise in accuracy. Also, this system is ineffective in the descent and approach phases because the flight path and speeds in descent are sensitive to changes in the cost index. For example, the cost index and descent path must remain substantially constant within the descent phase. Also, the descent speeds are more likely, in this system, to be impacted by an aircraft operational limitation because the descent speeds are more sensitive to cost index changes than the cruise speed. Also, the control may be unable to decrease the descent speed if the powerplant is already being operated at idle.
Attempts have been made to provide an active speed control which utilizes sensory feedback during various phases of flight. All such prior attempts, however, have failed for a number of reasons. The most significant obstacle is that the sensitivity of time of arrival to the climb and descent speed is difficult to estimate. Further, accomplishing desired changes to the climb and descent speeds when the aircraft is in these flight phases is problematic. The basic architecture of current flight management systems does not accommodate modifications to the climb and descent speeds when the aircraft is in these phases.
Therefore, it would be desirable to have an RTA control system and method that would enhance flight safety and provide increased aircraft autonomy by extending its capabilities from the cruise phase to climb, descent and approach.
It would also be advantageous to have an RTA control system and method wherein the method of speed adjustment could be chosen arbitrarily while maintaining acceptable control response time.
It would further be advantageous to have an RTA control system and method wherein the method of speed adjustment could be varied during different segments of the mission while maintaining acceptable control response time.
It would further be advantageous to have an RTA control system and method wherein the method of speed adjustment could be chosen in the cruise segment to minimize fuel consumption while maintaining acceptable control response time.
It would further be advantageous to have an RTA control system and method wherein the method of speed adjustment could be chosen in the descent segment to maintain speed adjustment flexibility late in the flight while maintaining acceptable control response time.
It would further be advantageous to have an RTA control system and method wherein the descent path could be planned to be more shallow than a fuel optimal descent, thereby allowing speed adjustments to be made during descent to accurately meet the time constraint.
It would further be advantageous to have an RTA control system and method wherein the system and method could model more subtle effects and non-linearities, such as the encroachment upon aircraft operational limitations, so that the system and method could quickly determine the most appropriate speed adjustment.
It would further be advantageous to have an RTA control system and method wherein the system would take full advantage of the full flight management system predictions system, and not simply the less accurate equivalent range approximation, so that the determined speed adjustment would be more accurate.
It would further be advantageous to have an RTA control system and method wherein the system would consider fuel reserves in determining the earliest achievable estimated time of arrival.
It would further be advantageous to have an RTA control system and method wherein the system would not suggest an earliest estimated time of arrival that would require the aircraft to accelerate to speeds greater that the speed that would cause the level of the fuel remaining at the destination to be below the minimum reserve.
It would further be advantageous to have an RTA control system and method wherein the RTA could be in the descent phase, below speed constraints and speed transitions, and the system would plan the speed profile to retain control authority for the longest possible period to reduce the risk of missing the RTA.
It would further be advantageous to have an RTA control system and method wherein multiple RTA waypoints could be entered, and the system would be able to select a speed profile to meet each RTA.
It would further be advantageous to have an RTA control system and method wherein the system would be flexible in its ability to accommodate RTA specifications in a variety of logical formats.
It would further be advantageous to have an RTA control system and method wherein the system would optimize the speed profile to minimize fuel consumption while meeting the time constraints.
It would further be advantageous to have an RTA control system and method wherein the flight segments that include airspeed decelerations in descent would be predicted with an off-idle throttle, and wherein the guidance system would accurately control the airspeed to match the predicted mission by dynamically changing the speed target that would be sent to the automatic throttle during the deceleration segment.
The instant invention provides a system for controlling the flight of an aircraft to meet an RTA. The system comprises a speed profile generator that communicates with a trajectory generator to produce a speed profile signal that enables the aircraft to reach a waypoint substantially at a predetermined time. In the system of the instant invention, the speed profile generator receives a nominal speed command signal, a time error signal and a sensitivity signal. Based on these inputs, the speed profile generator produces a speed profile signal. The trajectory generator receives the speed profile signal and a required time of arrival signal. Based on these signals, the trajectory generator produces a time error signal and a sensitivity signal. This sensitivity signal represents the sensitivity of the time error signal to changes in the speed profile signal.
The instant invention also provides a method of controlling the flight of an aircraft. This method comprises the steps of producing a time error signal in response to a required time of arrival signal and a speed profile signal, revising the speed profile signal in response to the time error signal, producing a sensitivity signal in response to the revised speed profile signal, and revising the speed profile signal in response to the sensitivity signal. Through this method, an aircraft is enabled reliably to reach a waypoint substantially at a predetermined time.